Boring of diversion tunnels during the construction of Boulder Dam in the Black Canyon of the Colorado River in the U.S.

Diversion tunnels made for the construction of Boulder Dam on the Colorado River in the United States. The dam site in the Black Canyon of the Colorado River. Rocks on either side of the river. A bridge on the river. A small tunnel on one side of the river. Several workmen at the mouth of the tunnel. Men operate drilling jumbos mounted on a motor truck. A man on a ladder. Workmen drill holes into rocks with drifter drills. Equipment for drilling. Trucks and power shovels in a bore to remove shattered material. A truck comes out of the tunnel. Workmen watch the truck. Trucks move in a line on a road along the canyon walls. The trucks dispose off wastes in gulches. Men at work in the tunnel. A man operates a concrete machine. A gantry crane is operated by workmen to lay lining of concrete on sidewalls of the tunnel. Men near movable steel forms. A man operates a machine.